Begin by letting u = 3x^2 and dv = e^(-x) dx. Then du = 6xdx and v = -e^(-x). Applying integration by parts,
Again, we cannot really integrate 6xe^(-x) dx without using parts, so we let y = 6x, dz = e^(-x)dx --> dy = 6dx and z = -e^(-x). Hence,
And just carry it out from there. Remember to add a constant when you are done, since antiderivatives are not uniquely determined and can differ by a constant.
